The present invention relates to a transmission power setting method, a data rate control method, and a reception method for use in a radio station in a wireless communication system that uses a broadband where the channel quality in a bandwidth tends to distribute unevenly and that uses a channel code.
To achieve a desired reception quality in a wireless communication system, a technology for controlling the transmission power of a wireless communication device is known. For example, U.S. Pat. No. 5,267,262 discloses a technology for allowing a base station to measure a signal reception power from a terminal and issue a transmission power increase instruction to a mobile terminal station when the measured power value is smaller than a desired value or a transmission power decrease instruction to a mobile station when the measured power is greater than a desired value, and for allowing a mobile station to control the transmission power according to the above-mentioned transmission power control instruction, thereby ensuring that the power received by the base station is virtually constant.
Another technology, which is disclosed by U.S. Pat. No. 5,559,790, is for enabling a mobile station to measure the reception quality of a pilot signal transmitted by a base station at a known power level and, based on the measurement result, to transmit a transmission power control signal to the base station so as to request a higher transmission power when the reception quality is poorer than when the reception quality is adequate and, at the same time, allowing the base station to control the transmission power for a signal directed to the mobile station in accordance with the transmission power control signal, thereby ensuring that the quality of received signals sent from the base station to the mobile station is maintained virtually constant for the mobile station.
The above technologies make it possible to provide consistent reception quality by maintaining the power received by a receiving station constant and avoid reception quality deterioration due to channel gain fluctuation and intra-system interference due to unduly high transmission power.
In a broadband communication system, the channel reception quality may vary according to the bandwidth because of the effects such as frequency selectivity noises and multipath interference. In such a case, there is a potential technology for performing communication at a usable data rate according to the quality of the channel of each bandwidth. In addition, JP-A-2001-186102 discloses a technology that measures noises in each bandwidth to select a bandwidth to which the transmission power is to be allocated, allocates data to the selected bandwidth to save power, and performs communication at a data rate usable for each bandwidth.